1. Field of the Invention
The invention relates to a processing method of a flat panel display apparatus.
2. Description of the Related Arts
As an image display apparatus in place of a cathode ray tube (CRT) that is a mainstream at present, various kinds of flat panel display apparatuses are being examined. As such flat panel display apparatuses, for example, a liquid crystal display apparatus (LCD), an electrolumescence display apparatus (ELD), and a plasma display apparatus (PDP) can be mentioned. A flat panel display apparatus in which a cathode panel having electron emitting devices has been assembled is also being developed. As electron emitting devices, a cold cathode field electron emitting device, a metal/insulating film/metal type device (also referred to as an MIM device), and a surface conduction electron emitting device have been known. Attention is paid to the flat panel display apparatus in which the cathode panel having the electron emitting devices formed by those cold cathode electron sources has been assembled from a viewpoint of a color display of high resolution, a high response speed, and high luminance and from a viewpoint of low electric power consumption.
The cold cathode field electron emitting display apparatus (hereinbelow, there is a case where it is abbreviated to a display apparatus) as a flat panel display apparatus in which the cold cathode field electron emitting devices as electron emitting devices have been assembled generally has the following construction. That is, a cathode panel CP having a plurality of cold cathode field electron emitting devices (hereinbelow, there is a case where they are abbreviated to field emission devices) and an anode panel AP having phosphor regions which are excited and emit light by a collision with electrons emitted from the field emission devices are arranged so as to face each other through a space which has been maintained in a high vacuum state, and the cathode panel CP and the anode panel AP are joined through a joint member in a peripheral edge portion. The cathode panel CP has electron emitting regions corresponding to subpixels arranged in a 2-dimensional matrix form. One or a plurality of field emission devices are provided in each electron emitting region. As field emission devices, a spindt type, a flat type, an edge type, a plane type, and the like can be mentioned.
For example, FIG. 7 shows a schematic diagram with a part cut away of a representative display apparatus having spindt type field emission devices. FIG. 8 shows a schematic exploded perspective view of a part of the cathode panel CP and a part of the anode panel AP at the time when the cathode panel CP and the anode panel AP are exploded. The spindt type field emission devices constructing the display apparatus include: cathode electrodes 11 formed on a supporting plate 10; an insulating layer 12 formed over/on the supporting plate 10 and the cathode electrodes 11; gate electrodes 13 formed on the insulating layer 12; opening portions 14 formed in the gate electrodes 13 and the insulating layer 12 (first opening portions 14A formed in the gate electrodes 13 and second opening portions 14B formed in the insulating layer 12); and conical electron emitting portions 15 formed on the cathode electrodes 11 locating in bottom portions of the opening portions 14. An interlayer insulating layer 16 is formed on the insulating layer 12. A focusing electrode 17 is formed on the interlayer insulating layer 16.
In the display apparatus, the cathode electrode 11 is a belt-shaped electrode extending in the column direction (Y direction) and the gate electrode 13 is a belt-shaped electrode extending in the row direction (X direction) different from the Y direction. Generally, the cathode electrode 11 and the gate electrode 13 are formed in such directions that projection images of both electrodes 11 and 13 cross perpendicularly. An overlapped region where the belt-shaped cathode electrode 11 and the belt-shaped gate electrode 13 overlap is an electron emitting region EA and corresponds to one subpixel. The electron emitting regions EA are ordinarily arranged in a valid region (a center display region which performs a display function as a practical function as a flat panel display apparatus; an invalid region is located outside of the valid region and surrounds the valid region in a picture frame shape) of the cathode panel CP in a 2-dimensional matrix form.
The anode panel AP has such a structure that phosphor regions 22 (specifically speaking, red light emitting phosphor regions 22R, green light emitting phosphor regions 22G, and blue light emitting phosphor regions 22B) having a predetermined pattern are formed on a substrate 20 and the phosphor regions 22 are covered with an anode electrode 24. Intervals among the phosphor regions 22 are filled with a light absorbing layer (black matrix) 23 made of a light absorbing material such as carbon, thereby preventing the occurrence of a color turbidity of a display image and an optical crosstalk. Each of the phosphor regions 22 constructing one subpixel is surrounded by partition walls 21. A plane shape of the partition wall 21 is a lattice shape (pattern like two pairs of intersecting parallel lines). Spacers 40 extending in the row direction (X direction), spacer holding portions 25, and joint members 26 are provided in the diagram. The partition walls and spacers are not illustrated in FIG. 8.
One subpixel is constructed by the electron emitting region EA on the cathode panel side and the phosphor region 22 on the anode panel side which faces the electron emitting region EA. Picture elements (pixels) are arranged in the valid region on the order of, for example, hundred thousands of pixels to millions of pixels. In the display apparatus which performs a color display, one picture elements (one pixel) is constructed by a set of a red light emitting subpixel, a green light emitting subpixel, and a blue light emitting subpixel. The anode panel AP and the cathode panel CP are arranged so that the electron emitting region EA faces the phosphor region 22 and are joined through the joint members 26 in the peripheral edge portion, and thereafter, they are evacuated and sealed, so that the display apparatus can be manufactured. A space surrounded by the anode panel AP, cathode panel CP, and joint members 26 is held in a high vacuum state (for example, 1×10−3 Pa or less). Therefore, unless the spacers 40 are disposed between the anode panel AP and the cathode panel CP, the display apparatus will be damaged by the atmospheric pressure. Generally, an antistatic film 40A made of, for example, CrOx is formed on the side surface of the spacer 40.
When driving the display apparatus, a line-sequential driving system is often used. The line-sequential driving system is a method whereby the electrodes in the group of electrodes which cross in a matrix form, for example, the gate electrodes 13 are assumed to be scanning electrodes (the number of scanning electrodes is equal to N), the cathode electrodes 11 are assumed to be data electrodes (the number of data electrodes is equal to M), the gate electrodes 13 are selected and scanned, and an image is displayed on the basis of a signal to the cathode electrodes 11, thereby forming one picture plane. In such a line-sequential driving system, the electron emission from each electron emitting region EA is executed only for a selecting time of the scanning electrodes, that is, for a duty period of time of the scanning electrodes. The duty period of time is equal to a time of a few seconds obtained by dividing a refreshing time (for example, 16.7 msec in the case of 60 Hz) of the frame by N.
More specifically speaking, a negative voltage is relatively applied to the cathode electrode 11 from a cathode electrode control circuit 31, a positive voltage is relatively applied to the gate electrode 13 from a gate electrode control circuit 32, and a positive voltage which is further higher than that to the gate electrode 13 is applied to the anode electrode 24 from an anode electrode control circuit 33. In the case of displaying by the display apparatus as mentioned above, a video signal is inputted to the cathode electrode 11 from the cathode electrode control circuit 31 and a scan signal is inputted to the gate electrode 13 from the gate electrode control circuit 32. Electrons are emitted from the electron emitting portion 15 on the basis of a quantum tunnel effect by an electric field that is caused when voltages are applied to the cathode electrode 11 and the gate electrode 13. The emitted electrons are attracted to the anode electrode 24, pass through the anode electrode 24, and collide with the phosphor region 22. Thus, the phosphor region 22 is excited and emits light and a desired image can be obtained. That is, the operation of the cold cathode field electron emitting display apparatus is fundamentally controlled by the voltage which is applied to the gate electrode 13 and the voltage which is applied to the cathode electrode 11.
When the electrons emitted from the electron emitting region EA locating near the spacer 40 pass through the anode electrode 24 in the anode panel AP and collide with the phosphor region 22, a part of the electrons are backwardly scattered in the phosphor region 22. A part of the back scattering electrons collide with the spacer 40. Thus, such a phenomenon that a gas adsorbed to the spacers 40 is released, molecules or the like of the released gas are adhered or adsorbed onto the surface of the electron emitting portion 15 constructing the electron emitting region EA locating near the spacer 40, and electron emitting characteristics in the electron emitting portion 15 are changed occurs. When such a phenomenon occurs, an amount of electron emission from the electron emitting region EA locating near the spacer 40 changes, so that a difference occurs between an electron emitting state in the electron emitting region EA locating near the spacer 40 and an electron emitting state in the electron emitting region EA which is not located near the spacer 40 (the electron emitting region EA locating at a position away from the spacer 40).
Such states are schematically shown in FIGS. 9A and 9B. An anode current value shown on an axis of ordinate in FIGS. 9A and 9B is a value of an anode current flowing between the electron emitting region and the anode electrode by the electrons emitted from the M electron emitting regions which occupy one row. An axis of abscissa indicates positions of the electron emitting regions along the column direction (Y direction). An alternate long and short dash line extending vertically in FIGS. 9A and 9B indicates positions where the spacers are arranged. In the example shown in FIG. 9A, an amount of electrons which are emitted from the electron emitting region locating near the spacer is larger than an amount of electrons which are emitted from the electron emitting region locating at a position away from the spacer. In the example shown in FIG. 9B, the amount of electrons which are emitted from the electron emitting region locating near the spacer is smaller than an amount of electrons which are emitted from the electron emitting region locating at a position away from the spacer. Whether the electron emitting state becomes the state shown in FIG. 9A or the state shown in FIG. 9B depends on the specifications or the like of the display apparatus. There is a case where a difference of luminance in the display apparatus lies within a range from a few % to ten and a few % depending on a difference between the amounts of emitted electrons. Such a problem that the picture quality is remarkably deteriorated and the spacer is visually perceived due to such a luminance difference also occurs.
An aging change occurs in the emitting state of the electrons from the electron emitting region. Such a state is shown as examples in FIGS. 10, 11A, 11B, and 11C. An anode current relative value shown on an axis of ordinate in each of FIGS. 10, 11A, 11B, and 11C is a value (unit: %) obtained by dividing (the value of the anode current in the electron emitting region locating near the spacer) by (the value of the anode current in the electron emitting region locating at the position that is sufficiently away from the spacer). An axis of abscissa indicates an elapsed time (although its unit may be arbitrarily set, it is shown by a logarithm scale). In the example shown in FIG. 10, although the anode current relative value changes together with the elapse of an operating time, its change amount differs depending on an initial anode current relative value. Moreover, when a long time elapses, the change amount is approximately converged into a certain value. For example, when the initial anode current relative value is equal to about 106%, the change amount changes to about 98%. when the initial anode current relative value is equal to about 100%, the change amount changes to about 96%. when the initial anode current relative value is equal to about 94%, the change amount changes to about 95%. when the initial anode current relative value is equal to about 90%, the change amount changes to about 96%. It will be understood from FIGS. 11A, 11B, and 11C that change ratios (inclinations of straight lines in FIGS. 11A, 11B, and 11C) of the anode current relative value to the time differ depending on the initial anode current relative value.